i think that he might have misspoken or at least been misunderstood. I don't think that it's the iPod that is coming to an end, more as the mystique surrounding it.
Consider this:
The iPod was certainly not the first mp3 player, i believe that the RIO cd/mp3 player was the "first" (this is going way back). The iPod is what made it very cool to own an mp3 player.
That's always been the thing with Apple products. They are kinda like a "members only club", where owning one makes you feel elite and cool. Looking down on the windows peons who have yet to be enlightened.
Everyone owns or has owned a windows machine at one point or another. But only the "special" few select people can own an APPLE. So there is a factor of exclusivity to it.
Now that Apple has a considerably larger market share in just about everything, that exclusiveness is starting to disappear. Now instead of the elite owning an iPod, Joe Schmoe has an iPod. And with the incredibly good price for the iPhone, it is quite honestly the absolute best value for your dollar regarding mobile phones.
It even blows the windows mobile PDA out of the water, and I own a windows mobile PDA!
And because of the iPod and the iPhone, more and more people are looking towards OS X as a computer system as opposed to Vista.
...well Vista kinda helped with that one a bit too when it first came out...
So i think what he was getting as wasn't so much that their (Apples) reign as king is coming to an end, but that there exclusiveness is becoming more and more common and less exclusive.
Another way to think about it is like this. Way back in the day when it cost $10,000 for a computer with an 8 meg hard drive there was a serious amount of exclusiveness to it.
Not only did it cost the same as 2 years college tuition, but you really had to know what you where doing and want to learn. No point and click, no pretty gui, all command line. Sure there were some games out there (Tapper, and the old Sierra Games), but mostly people gamed on Atari and NES.
There was no "internet" as we know it today, so we were all stuck with word of mouth, exploration, reading thick and boring manuals, BBS' if you were lucky to have a modem and many many "Oh Fuque" moments.
I still remember typing in Format C

in Dos with no parameters....
Talk about exclusiveness. It was like holding the holy grail of knowledge cause you had a computer!
(not typing format c, but knowing how to use a word processor or a spread sheet)
And then eventually the price dropped and more and more people bought them.
Then Windows 1, and then 3.1 came out, and suddenly things got easier. But as they got easier people started to take them for granted. And you no longer had to know what you were doing and just be stupid about things.
(i just fixed a girls computer cause she clicked on the link that said "give us your credit card and we will remove all 9000 viruses on your computer". And she gave them her CC! Then she let her friend who is in school for "computer sciences" or some B.S. "Fix" it. I just love people who blindly delete registry keys...)
Today, everyone owns a computer, and most people don't have a clue as to what they have or even have an interest in making it work. So I think that is where Woz was going with that, that the exclusiveness is disappearing.
All and all where could it go next? We are all so concerned about smaller size and bigger capacity that we really do have the best there is. Other changing compression formats (mp3, ogg, flac, m4a, aiff and so on) And having more storage on the cheap, and tweaking the GUI. The most we can hope for it upgrading to thinner and prettier. And then there is the point where it can't go any smaller because it just becomes unusable.
And the MP3 concept has been around for 20+ years and it's now just become common.
If anything, the only thing that i could see happening would be having holographic projectors the size of a phone for video conferencing. Or implants that are connected to a massive data base that you merely need to think it and you have it.
But who knows? I am certain that it will come out eventually, but i doubt any time soon.
*****edit
Unless of course someone creates the "Dawson's Creek Trapper Keeper Ultra Keeper Futura S 2000" like in South Park.